Protective suits may be required to protect the wearer against a variety of chemical and biological agents. For example, protection is required against droplets of certain agents which may affect the skin, and against vapours of the same or other agents which are a threat to the respiratory system. Toxic biological agents may be in the form of spores and are therefore a particulate threat, which can only cause casualties if inhaled or if allowed to penetrate into the body through an open wound. There are also biological agents which present a hazard if they are delivered in the form of a liquid agent which can penetrate the skin.
Heat stress is universally recognised as being the greatest limiting factor for the achievement of a suitable protective clothing system. Attaining total chemical protection in a clothing system is not difficult. Impermeable materials such as butyl rubber are available to give such protection. However, any non-breathable clothing system will prove unwearable under most conditions in a matter of minutes. It is no good providing total protection if it results in the wearer losing his effectiveness.
It has therefore been attempted to develop an anti-gas fabric which not only protects but which allows air to penetrate and water vapour from the body to permeate out. Filtration of the chemical liquids and vapours is therefore required, and activated carbon is a well-known and effective adsorbent.
All clothing systems need to be flexible, and therefore early development revolved around impregnating a suitable textile carrier with activated carbon adhered to it, i.e. creating a synthetic activated carbon material. Many approaches have been developed: impregnated polyurethane foam, non-wovens with bonded charcoal, carbon-filled spheres bonded to a carrier material. All of these approaches have two major limitations, i.e.
a) inability to provide sufficient carbon on the surface of the carrying material without blocking off its breathability; and PA0 b) degradation of the charcoal due to aging of the bonding process.
Other common limitations present in some or all of these systems are: shedding of charcoal through abrasion, lack of launderability and, most important of all, lack of breathability and high thermal insulation properties.
There are different aims reflected in known protective clothing systems. Each system reflects both the technology available and a particular protection philosophy.
For example, if it is decided that very high protection levels are necessary, an anti-gas system may be based on a polyurethane foam loaded with activated carbon powder. The disadvantages encountered by such a system are as follows: the high insulation properties of the polyurethane foam make the physiological load on the wearer undesirably high, and the high carbon loading necessitated by the high protection factor increases the weight of the garment and reduces its breathability, and therefore also increases the physiological load.
An alternative aim is to balance adequate protection and a reasonable physiological burden. To this end, a known anti-gas fabric is a fluorochemical-treated non-woven which has been coated with fine active carbon particles fixed with a polymeric binder. However, although the physiological burden on the wearer is reduced in this case, the protection offered by this system is not sufficient to allow it to be worn as an integral uniform, only as a protective overgarment.